Once the spline cutting jig was assembled and tested it was now time to cut the slots along each edge of the boxes. This process went very smoothly. The jig took some time to make but made this very nice detail incredibly easy to accomplish. Notice the look I was after was to have all three boxes with the same spline pattern.
Here is a shot of two of the boxes with the glue filled splines inserted. Now we just need to wait for them to dry. Because I cut them oversize (I didn't want to bother cutting them precisely to size) I will later need to trim them with a back saw or dovetail saw. This worked out OK but ended up being a lot of manual cutting (120 cuts in all for 3 boxes!). But it wasn't that bad. In the future I would recommend cutting these splines more uniformly and closer to actual size needed and just sand as needed.